Hydraulic slip compensating valve



2 Sheets-Sheet 1 Nov. 22, 1960 E. E. WAGNER HYDRAULIC SLIP COMPENSATING VALVE:

Filed July l2, 1957 in 1x4/ @4% W h mv WIGE w@ Nov. 22, 1960 E. E. WAGNER HYDRAULIC SLIP CQMPENSATING VALVE 2 Sheets- Sheet 2 Filed July 12, 1957 United States Patent() HYDRAULIC SLIP CMPENSATING VALVE Ernest E. Wagner, Santa Ana, Calif.

Filed July 12, 1957, Sel'. N0. 671,468

10 Claims. (Cl. 137-487) This invention pertains to pumps, hydraulic motors and related equipment in hydraulic circuits in general and to means for compensating for variations in the output speed of hydraulic motors, the output volume of pumps and the volume of uid flowing in hydraulic systems and it has particular reference to a device for compensating for said variations when caused by changes in uid pressure (p.s.i.) which, perforce, cause proportional changes in the volume of iluid slipping past capillary clearances between moving and movable parts in the circuit which may be subjected to a pressure differential.

The object of the invention is to provide a means for offsetting the effect of hydraulic slip past the capillary seals, thereby to prevent hydraulic motors from stalling at slow speeds and variable delivery pumps from ceasing to deliver uid when set to pump small quantities.

A further object of the invention is to provide a device by which controlled quantities of fluid may be subtracted from a fluid circuit to odset the disturbing effect of any variation in slip past the capillary seals and thereby to hold the output of hydraulic motors and pumps uniform at a reduced capacity.

A still further object of the invention is to provide a device by which metered quantities of fluid may be added to a hydraulic circuit to cancel the disturbing effect of variations in slip past the capillary seals, caused by variations in pressure, and thereby maintain the output of hydraulic motors and pumps uniform at maximum capacity.

Another object of the invention is to provide a metering instrument capable of automatically metering liuid in or out of a hydraulic circuit or system in such proportions that the rate of operation of hydraulic motors and pumps in the system will not fluctuate under load changm ranging from no load to full load.

An additional object of the invention is to provide a device of the character referred to in which the rate of flow for a given pressure may be readily varied.

These and other objects are accomplished by a form of device shown, in preferred form, in the accompanying drawings, in which:

Fig. 1 is a longitudinal section through the valve on line 1 1 of Fig. 2.

Fig. 2 is a cross section on line 2 2 of Fig. 1.

Fig. 3 is a section on line 3 3 of Fig. 2, showing the vertical disposition of the various openings and passageways.

Fig. 4 is a partial cross section on line, 4 4 of Fig. 1, showing the position of the various pasasgeways relative to one another after removal of the center rod and diierential plunger.

Fig. 5 is an enlarged fragmentary cross section through the capacity control device, which is shown with its channels in a position of minimum capacity.

Fig. 6 is an enlarged fragmentary cross section, similar to Fig. 5, showing the channels in a position of maximum capacity.

Fig. 7 is a schematic representation of Fig. 1 without the center rod.

Fig. 8 is a circuit diagram showing a slip compensating valve and a hydraulic motor in parallel and their respective presure vs. slip diagrams.

Fig; 9 is a schematic representation of the passageways of a slip compensating valve for bleed-out service.

Throughout the drawings, similar reference numerals designate similar parts.

The symbols PL, Po and Pc, alone and in combination, are used in the drawings and specification to facilitate a clear understanding ofthe instrumentality and its operation. They denote the following:

PL, the pressure registered in p.s.i. gauge on the high pressure side of a pump or hydraulic motor under load.

PL max., the maximum operating pressure for which the valve is designed.

Po, the pressure registered in p.s.i. gauge on the low pressure side of a unit.

PL-Po, the pressure differential representing the working load on the system.

Pc, the control pressure in p.s.i. generated by the hydraulic slip compensator in response to the pressure differential PL-P0. Pc, is a gauge pressure only for Po gauge=zero.

VSC, hydraulic slip-compensating valve.

The construction of the valve is identical for both bleedin circuits circuits to which a controlled quantity of fluid is added-and bleed-out circuits circuits from which a controlled quantity of fluid is subtracted-and, provided the valve, in all its parts, is designed to withstand the maximum pressure likely to occur, it may be employed for either service. The description will, therefore, be limited to the use of the valve for bleed-out service and, furthermore, it will be limited to a valve for holding the `speed of a hydraulic motor at constant r.p.m., though subject to the disturbing influence of a varying load (torque), for the reason that the same valve will perform equally Well when used for holding constant, the rate of ow of a pump, though subject to the disturbing iniluence of a varying load (p.s.i.).

Reference is made to Fig. l, wherein is shown a valve comprised of 3 pieces or sections, 11a, 11b, and 11C, which are joined together by bolts 12 and 12a substantially as shown in Figs. 1 to 4, to form a valve body having covers 15, 16 at the respective ends thereof, said covers being secured in position by said bolts 12, 12a.

A housing 13 is bolted to the center section 11b of the valve body. Said housing 13 is provided with a bore 86 in which is disposed a pressure control valve spool S5 that is adapted for operation relative to an inlet port 46 and an outlet port 42 in said bore. Both ends of the bore 86 are closed respectively by plugs 90 and 91, which thread into the housing 13 and are sealed by O rings 92 and 93 respectively. Each plug 90 and 91 is provided with a piston 94 and 95 which bears against the respective ends of and are adapted to actuate said valve spool 85. Said plugs and 91 are provided with fluid inletoutlet passages 96 and 97 respectively.

The housing 13 is provided with a threaded inlet passageway 17, Fig. l, which communicates, via passageway 9S in the center section 11b, with coaxial, longitudinal passageways 1811, 18a and 18o, which form a continuous passageway throughout the valve body and through which iiuid is conducted from the inlet 17 to the caps or covers 15, 16 which, in turn, are in communication with differential plunger sections 21 and 23 respectively. Passageway 18h also communicates via passageway 41 with the port 40, heretofore referred to.

The valve body sections 11a and llc are provided with concentric differential bores 19 and 20 respectively the latter bore being the smaller-for guiding a diifer,

ential plunger composed of integrated sections or members 21, 22, 23, preferably threadedly connected together. Reference to a differential plunger, hereinafter, shall be understood torefer to the integrated structure consisting of sections 21-22-23. Section 21 of the differential plunger is a smooth surfaced; tubular member having a close sliding fit in bore 19. It is threaded internally at one end toreceive an externallyn threadedend 103 Yof the center section 22 which has a hole 100 extending centrally throughout its length and which is provided, atY each end, with internal threads 101, 102. Upon a portion of thesperiphery of section 22 are formed serrations 49 that cover the entire circumference and are adapted to mate with serrations 48 concentrically arranged within the center section 11b of the valve body; Figs. 5, 6.

The upper Vinternal thread 101 in the center section22 receives a fitting 64, threaded externally on both ends, one end to fit thread 101 and the other end to thread into one'end of an extension spring 89, concentrically disposed within the hollow member 21 of the differential plunger, thereby to connect the differential plunger and spring together.

The extension spring 89, at its opposite end, is in turn threaded onto a calibrator fitting 62 suspended from an antifriction bearing 6 3 mounted in a threaded sleeve 65, adjustable axially within the Valve body section. 11a, so that the differential plunger, after the spring is calibrated, can be raised or lowered relative to the channels between the sei-rations 48 in the valve member 11b. The lower internal thread 102 of section 22 receives Vthe external, mating thread of the plunger head, section controlled amounts of fluid: The effective differential action on the differential plunger is proportional to the product of the difference in the areas of the plunger sections 21 and 23 and the pressure differential PL-Po. The pressure PL acts externally on the differential plunger from opposed ends, Fig. 7. The pressure Po acts within the chamber r35 opposing entrance of the plunger 19 into the chamber.V TheY pressure P0 acts within an annularl space or chamber 46, provided in thevend of the center section 11b, therefore the area of section 23 and section 22 must be equal to avoid imbalance under the inuenceof the control'pressur'e Pc.

The area ofthe serrated or channeled outline 49 of l the plunger section 22,' Fig. 6, can be reduced to an equivalent area of smooth diameter. For serrations having an outline corresponding to that of conventional gear teeth the equivalent smooth diameter is slightly larger than the pitch diameter butsmaller than the O D.; it lies between the two. In Fig. ,7,. 49a represents the equivalent smooth diameter of the channels Vor teeth 49 of section 22. The equivalent smooth diameter 48a of the internal teeth 48'must, perforce, be equal to the equivalent smooth .diameter 49a of its mating external 24. Y, The fitting 64 in the upper end of section 22 also v has a hole 104 through it, concentric with the axis of the differential plunger and it also forms a sliding capillary seal with the central member 24 and thus'provides an annular space 37'within the center section 22, which is'delined by the central member 24 the hole 100 and the two capillary endseals 104 and 105. v

Y- The'central. member 24, Fig.. l, extends from a point near the bottomcover 16, through the differential plunger to apoint beyond the capillary seal 104, as shown,-and near the bottom thereof is provided with a control pressure port 99 which is connected to the aforementioned spool actuating piston 95 by passageways 25 in said central member 24, passageway 26 within a tube 31 disposed in a clearance hole'106 in an end of the Vcentral member, passageway 27 in the cover 16, Figs. 1, 2, 4, passageways 28cland 2817 in the body sections 11o and 11b, passageway 29 in 11b, Fig. 2, passageway 30 in block 13 and passageway 97, heretofore referred to, in the plug 91. Saidrspool actuating piston 95 is adapted to operate the pressurel control' valve spool 85 in a manner, as hereinafter described. v e A housing'14 is provided with a threaded outlet 32 for connection with the low pressure side of a hydraulicY system in which the valve is to operate. Outlet 32 communicates'outlet pressure P0, via passageways 33 in the housing and 34 in the valve body, to a chamber 35 within the valve body section 11b. The chamber 35 is in communication with the annular space 3.7 via passageways 36 passingthrough the walls of sections 21 and 22 of' the differential plunger. As the central member 24 is of equal diameter throughout, pressure in theannular space .37 has Yno eect upon the action of the differential plunger,but the outlet pressure P0 is brought to bear upon surface 38, which is the inner end of the plunger head 23,- for'reasons presently explained.

Y Particular attention is drawn to the following in connectinfwith'the, forces operating to automatically meter teeth. Plunger diameter, section 23, has been made equal to the equivalent smooth diameter 49a, therefore, the areason both sides of the chamber 46 having been made' equal no disturbing action by the control pressure Pc is possible, furthermore, the diameter 49a in the chamber 35 being the equivalent of the diameter ofthe channels or teeth 49, section 22, the effective differential action of the differential plunger assembly 21-22-23 is preserved. It has also been shown, hereinbefore, that the pressure Po in the annular space 37 is fully balanced, therefore, Fig. 7, is in principle, the equivalent arrangement of Fig. l in respect to the forces acting upon the differential plunger.

With the aid of Fig. 7, the forces acting on the differential plunger are plainly evident. The area of section 21 minus section 23 or the equivalent area thereof; namely section 22'in the chamber 35, is under the linuence of the net pressure of PL-Po. The twoarea times psi-produce a force which is opposed by the tensiontof the extension spring 89. With an increase in IDL-P0 the differential plunger moves downwardly, with reference to Fig. 7, until the increasing tension in the spring restores a balance and vice versa. Considering the foregoing and theV characteristics of springs, it is evident that movement of the differential plunger is pro portional to the net pressure PL-Po.

- The capillary seal -defined by the hole 105 in the plunger head, section 23, the central member 24 and the distance between the ends 38 and 39 of section 23--is an integral part of the differential plunger and therefore traverses upon the stationary central member 24 in'vaiy ing amounts proportional to the pressure diiferential PL-Po-' y Y y .Port 99 in the rod 24 is so positioned that the sur# face 39 coincides with the edge of theport 99, as shown, whenever PL-Po equals zero. The spring 89 is so proportioned that the position of surface 38 opposing surface 39 .ofthe seal 105 coincideswith the opposite edge of the port 99,-whenever PL`P0 equals the' maximum pressure PL max. for which the valve is designed.

Whenever the capillary seal 105 moves along the mem.i ber 24,V thevport 99-being stationary-is spacedvary- Ying distances, proportional torPL-Po, from the shoul.

' pressure Po equal 'tov zeroY gage the control pressurel'lq will vary from zero, for PL-Po equal to zero, toamaxif mum equal to 25% of PL max. for PL-Po 'equal' t 5 PL max/2, after which it again returns to Pc equal t zero for PL-Po equal to PL max.

Bleed-off or bleed out uid may -ow from the inlet port 40 around the neck of the valve spool 85 to the outlet port 42, thence via passageways 43, 44 and 45 to the chamber 46 in the center section 11b of the valve body. From chamber 46 the tluid flows with, negligible resistance through an annular space formed by a neck 47 in section 22 and the internal channels formed by the teeth 48 in the valve body,rsection 11b, until it encounters viscous tlow passageways 50, Figs. and 6, formed between the internal channels or teeth 48 provided in the valve body and the external channels or teeth 49 provided on the diierentia'l plunger section 22, the two sets of teeth telescoping varying amounts and thereby varying the length of the viscous tlow passageways proportional to the pressure diterential PL-P'o for reasons appearing later.

The pressure in the chamber 46 must at all times be equal to the control pressure Pc inthe port 99 of the central member 24, irrespective of the volume of tluid the valve is called upon to meter out. For the purpose of checking upon the pressure in the chamber 46 so as to maintain the required control pressure Pc in accordance with the requirements dictated by the pressure diierential PL-Po, pressure in the chamber 46 is conducted via passageways 51, 52 and 53 in the valve section 11b, Fig. 2, passageway 54 in the valve block 13 and passageway 95, in the plug 90, to the spool actuating piston 94, thereby, to actuate the pressure control valve spool 8S as hereinafter described.

Seepage from the spool 85 and the pistons 94, 95 is collected in the end spaces 54, 55 of the spool bore 86 and carried from there to the low pressure side of the system via dual passageways 56, 57 in the housing 13 `and passageways S8, 59, 60 in the surface thereof, as shown in lFigs. 2 and 4. Passageway 61 in section 11b of the valve body carries the seepage fluid from passageway 60 to the chamber 35, in turn, communicating with the outlet 32 in the housing 14 via passageways 34 and 33.

A variation in the capacity of the valve may be achieved by varying the distribution of the clearances between opposite sides of the serrations or teeth 49, and means for accomplishing this include a toothed lever 73, pivoted at 74 in the housing 14, which is inserted into the center member 11b through an opening 75, until the tooth 76 on the end of the lever is in mesh with the gear teeth 49. Lever 73, on the end opposite the tooth, is machined spherically as shown at 88. The spherical surface S8 rides upon the internal surface of a conical bore 77, machined in the end of a regulating screw 78, which is provided with a seal in the form of an 0 ring 79 and a hexagon socket St) in its outer end by which the regulating screw can be moved in or out and thereby swing the toothed lever 73 upon its pivot 74, which action moves the external teeth 49 on the plunger section 22, circumferentially and relative to the internal teeth 48 in the body member 11b thereby varying the spaces between said'teeth, which spaces actually are viscous tlow channels and hence the capacity of the valve. This arrangement in no way interferes with the required axial movement of the dilerential plunger.

Without describing the functioning of the capacity control until later but assuming the setting to be as shown in Fig. 5, which is the position of minimum capacity, a position in which the teeth are so aligned that the clearance between them is equally dividedone-half on one side and one-half on the other side of each tooth-it will be found that the rate of flow through the valve is controlled as a function of PL-Po, that operation is fully automatic and attained in the following manner:

A torque load imposed on the output shaft of a hydraulic motor will result in an increase in PL-Po in the hydraulic system which increase is communicated to opposite ends of the differential plungerV and forces it to move until a balance is re-established between Athe hydraulic force and the opposing force of the extension spring S9, as hereinbefore described.

Movement of the differential plunger changes the control pressure Pc in the port 99 of the central member 24. A change in Pc is communicated tothe pressure control valve in housing 13, there to act on the spool actuating piston 95. Opposed to piston is the piston 9,4 inY communication with chamber 46 by passageways previously described. The direction in which the valve spool 85 will move depends upon which piston, 94 or 95 exerts the greater force.

In this connection, attention s again drawn to several important functional relationships of the valve, namely: 'Ihe manner in which Pc varies; 'increasing rst, then decreasing as PL-Po continues to increase.- For bleed-out service the length of the viscous Vpassageways 50 increases proportional to the yincrease in PL-PQ, while the volume of fluid QBo metered out decreases inversely proportional to PL--Po. The operating pressure PL minus the control pressure Pc, that is PL-Pc, represents the pressure across the orifice of the inlet port 40 of the pressure control valve. For an increasing load on the unit there is a proportional increase in the operating pressure PL, which, however, increases at a faster rate than the control pressure Pc; therefore PL-Pc increases more and more rapidly as PL increases. The net result is that for bleed-out service the orice area of the control valve, between spool S5 and port 40, must be progressively reduced by smaller and smaller increments for an increasing PL-Po and vice versa. The interaction of these variables is more readily visualized by expressing the relationships algebraically. It can be shown that:

QB0=Volume of uid metered out by the slip compensator proportional to PL max.-PL.

LV=Length of viscous tlow channels or passageways 50,

proportional to PL-Po.

LV max. Max. length of LV for PL-Po=PL max.

K=A constant based on the proportions of the cross section of the viscous flow channels 50.

PL Lv max. 13C-PL@ PL max.) LV-PLPL max.

By inserting the above last two values in the rst for'- mula, the rate of iiow is shown to be:

PL) Lv max. l

The last expressionA shows that the volume QBo flowing is inversely proportional to the load PL, a prerequisite for bleed-out service. Lv max. is fixed. Changing K (channel cross section) changes -QB0, -the vvolume metered out for a given-pressure. v

The correct value 'of the control pressure'rlc is generated in the'valve in the port 99, "likewise, the correct value for the channel length Lv'by the telescoping action of the channels 48 and 49, and both values have been shown to be proportional to PL-Po. Pc and Lv are continuously combined in the chamber 46 and its extension with the internal teeth 48, with the result, that the correct control pressure acts on the correct length of channel or passageway, which has been given 4a 'cross section dimensionally proportioned so as to be 'numerically equal to K and thereby automatically meter out the correct volume 'of iluid for a given pressure differential PL -Po.

From the foregoing it is evident that a change in cross section of the ow channels 50 will change lK and thereby alter the volume rate of ow for a given pressure without altering the characteristics of the valve in any QBo: (PL max.

scope? 7 other re'spet.m The positions "of the. teeth rforr'naximum andv hforminimum' ow are shown in Figs.16:'and 5 rel' 'spectively The ratio vof maximum( ow to minimum flow is4: l, since iluid liow in capillary channels of rectangular-,form is proportional to the cube ofthe depth of the channel.

Fluid conducting passageways in the valve are indicated diagrammatically in Fig. Y9. Passageways intended tou transmit pressure primarily, extend from theport 99` viav cover 16. to the plunger 95 and from the chamber'` 46 to the plunger 94.

Fluid enters the valve from the systemrat17tunder the intluence vof PL-Po and flowsV to and vexerts pres-` sure upon the differential plunger sections 21 and 23. At. the same time fluid -ows to the pressure control valve spool 85, in varying amounts, as demanded by PL-Po. `An increase in pressure in the system causes the differential plunger to move down-bore 19 being larger than bore 20therefore, uid is taken into bore 19, discharged from bore 20 up the passageways 18a, b .c to the bore 19 which, however, requires more iluid than is discharged from 20, consequently some Huid will have to be taken in from the system, a relatively small amount only being needed, as the two bores have only a small difference in diameter. The lluid owing continuously to the spool 85 is conducted from port 40, via port 42, to the annular space 46, thence through the ow regulating passageways 50, formed by the teeth 48 and 49, Figs. 5, 6, to the cham# ber 35V and from there to the outlet 32 to return to the system.`

Under the inuence of the working pressure PL in the bore 20 and the outlet pressure Po in the annular space 37, viscous flow takes place between the central member 24 and the capillary seal 105, thereby generating the correct control pressure in the port 99, which is transmitted to the piston 95. Fluid ow from the port 99, Fig. l, to the piston 95, Fig. 2, must be kept as close to zero 'as possible, to preclude the possibility of generating a distorted value for the control pressure. t

Another pressure transmitting line brings the pressure in the annular space` 46 to bear upon the piston 94.

Fluid ilow in this line must also be kept to a minimum to limit pressure drop.

Referring to Figs. l and 2, and yassuming that the valve is operating, c g., under a torque load represented by PLPo1=lO0 p.s.i. and .that the valve spool 85 and the differential plunger are correctly positioned for such a load, them-upon `encountering an increased load, the system will react by an increase in PL-Po as evidenced by an increase in PL at the inlet connection 17, which forces the dierential plunger down, with the result outlined above. Acceleration and displacement of the differential plunger :requires time, not much, however enough to result in a perceptible lag between the arrival of the full increase in Pc beneath the spool actuating pistou 95 and an increase in PL in the port 40, the latter, for all practical purposes, takes place instantaneously. The increase in PL in the port 40 is transferred to the chamber 46 and from there to the spool actuating piston Y 94. Build-up of pressure between the two points 40 and 94v iSsomeWhat cushioned by the ilow of fluid being metered out via thevviscous passageways 50. This latter action is to a good extent oset by the downward movement of the differential plunger and the consequent increase in resistance of the passageways 50 due to telescoping, which action, of its own accord tends to raise thepressure in the chamber 46. Since the increased loaden the system results, rst, in an increase in the force exerted by the piston 94 over that of piston 95, the valve spool 85 will move to close the port 4t) somewhat Aand thereby reduce the pressurek in the chamber 46 andbeneath the piston 94 until balance is reestab# lished.v If the valve reduces the ow through the port 40 to less'than that required-to hold 'the pressure in the chamber 46 to the proper value against theiiuid being meteredout, thenythe pressure in the chamber 46 and against the piston 94 wi'll'drop. 'As soon as the force on piston 94fis less than that on piston 95, the pressure of the latter being controlled independently by PL-Po, as hereinbefore explained in detail, the valve spool 85, will be forced to open somewhat until a balance between the two pistons is attained and the pressure in chamb er 46 corresponds-to Vthat in the control pressure port v99.L Operation is therefore fullyv automatic and in direct response to load changes on the'system.

The. immediately foregoing description pertains to the' operation of the valve upon encountering a load increase. A decrease in the load on the system is reflected by al decrease n PL atV the inlet tothe valve, in response to which the valve increasesV theV volume of uid owing through it. In response to the pressure change the valve spool must open progressively greater and greater amounts as the pressure continues to decrease. The sequence of events is such that the pressure in the chamber 46 will drop rst, reducing the force of the piston 94 below that of the piston 95 and thereby opening the valve. spool 85 until the pressure again balances, sub.- stantially the same as for an increase in pressure, except in reverse order.Y

' A fact, generally overlooked, is that speed variation in a hydraulic motor, with load changes, is unavoidable and occurs irrespective of all provisions made to hold the volume of uid delivered to the unit at a constant rate.- 'Ihe use `of standard llow valves, pressure compensated, is accepted practice but they cannot fully compensate for speed fluctuations with load changes. l It is readily apparent that any change in the volume of the uid flowing to aunit will cause a corresponding change inthe output speed of any hydraulic motor in the circuit. What is not so apparent is the fact that for a constant flow of oil to a unit, irrespective of the means by which it is kept constant, there is still a variation in speed with a change in load and that this variation is due to internal slip. In a circuit of the type supplied with a constant volume of fluid by means of a pressure compensated flow control valve, the addition of a slip compensator in parallel with the hydraulic motor will result in a constant speed output forV anyload from no load, to full load,.as presently explained:

In the foregoing the operation ofY and the means by which thev valve is caused to function automatically has been outlined and it Lhas been shown that the output of the valve is opposite to the normal output of capillary passageways under hydraulicpressure namely: Fluid ow through the valve decreases proportionally to an increase in pressure, whereas, the normal course of action is for the flow to increase proportionally to pressure. The output of the valve is therefore inversely proportional to that of-normal capillary action. The design and the characteristics of the valve are dictated by the requirements of the method employed to compensate for speed variations which are due to hydraulic slip, Vwhich is an inherent characteristic of hydraulic equipment of the type wherein fluid under pressure is restrained from free flow by capillary clearances between moving or movable parts.

In a positive displacement hydraulic motor, flow through capillary clearances under pressure results in a volume of fluid slipping through the clearances which is known as the slip volume Qs or slip and which is proportional to PL. See Fig. 8. Dividing the slip volume in cubic inches per minute by the displacement per revolution of the rotor in cubic inches results in a figure expressing the slip in rpm. Obviously, as PL increases Yso will the slip r.p.m. and, providing fluid flow to the unit is constant, the output speedmust perforce decrease a like amount. Y

In the lhydraulic slip `eorl'rpt-.nsator the volume QBo meteredout is inversely proportional to PL, see Fig. 8, and therefore proportional to PL max.-PL, consequently;

asados# for an increase in PL thereis a proportional decrease in the volume QBo metered out.

Fig. 8, applies alike to circuits including a' hydraulic motor or a pump. For a hydraulic circuit, embodying a hydraulic motor, fluid ow through the motor coincides with the direction of the arrows marked M. Flow through the slip compensating valve can only be from PL to Po (from high to low pressure). The function of the equipment being compensated is immaterial, metering is always inversely proportional to pressure.

Assuming, as an illustration, that a hydraulic motor is operating in a circuit in which a constant rate of uid ow is continuously maintained irrespective of pressure fluctuations, then the hydraulic motor will run at a constant speed only as long as there is no pressure change. When the hydraulic motor encounters resistance an increase in pressure in the system will result which will have no effect on the total volume of fluid llowing-since it was stipulated that the volume owing is to remain constant irrespective of pressure changes-but the slip r.p.m. of the hydraulic motor will increase' and therefore the speed of the unit decrease.

By placing a hydraulic slip compensator in such a circuit, in parallel with the hydraulic motor, the equivalent of additional slip is added to the circuit by the valve, see slip diagrams, Fig. 8. The differential pressure PL-Po is the same in both legs of the circuit, therefore, a given pressure PL will result in a total slip volume amounting to the motor slip volume Qs, plus the bleed out volume QBo, the sum of which is equal to Qs max. From Fig. 8 it is evident that Qs plus QBo always equals Qs max. irrespective of the pressure. Qs max. is a constant for the system. By converting the slip volume Qs max. to slip r.p.m. and subtracting the so derived slip r.p.m. from the theoretical r.p.m., the true output r.p.m. for the motor is obtained. Particular attention isV called to the fact that a variation in pressure no longer causes' the slip r.p.m. of the motor to vary. The unit runs at a slightly reduced speed, that is, somewhat slower than the maximum theoretical value, but it runs continuously at a constant output speed7 irrespective of pressure variations.

Response to a change in the volume of iluid sent to the hydraulic motor, whether an increase or a decrease, is immediately reflected in a proportional increase or decrease in r.p.m. and speed changes due to changing torque loads are automatically cancelled. Hydraulic motors are also prevented from stalling at extremely slow speeds, due to sudden load changes. Likewise variable delivery pumps will not stall, that is, fail to deliver uid 4against an increasing discharge pressure when they are set to deliver small quantities of fluid, as explained below.

ln the opening statement it was pointed out that the same valve, without regard to pressure variations, may be used for holding the speed of a hydraulic motor constant as well as for holding the rate of flow of a pump constant. Not only are the details of construction and operation identical for bot-h services, but in the majority of the cases which incorporate a pump and a motor in a common hydraulic circuit, a single valve will control both units.

Assuming, as an illustration, that a pump is operating in a hydraulic system in which the speed of the pump is kept constant, regardless of load fluctuations, then the pump will deliver fluid at a constant rate as longV as there is no change in pressure. Whenever the fluid delivered by the pump encounters more resistance the pressure in the system will increase. This will have no effect on the speed of the pump-since it was stipulated that the speed is kept constant irrespective of load changes-but the hydraulic slip of the pump will increase proportionally to the increase in pressure and therefore the net delivery decrease in proportion.

The slip r.p.m. is as useful a concept in connection with a pump as it is in connection with a hydraulic motor. Applied to a pump the slip r.p.m. represent a l@ loss in delivery equivalent to the loss of an equal number of r.p.m. Numerically the volume lost will equal the slip r.p.m. times the actual displacement of the rotor in cubic inches per revolution.

If a pump and la motor are alike in all essential dimensions, then the slip r.p.m. will also be the same, therefore, the reduction due to slip, in the output speed of a transmission consisting of the two, will be 2 times the slip rLpJm. The pump will fall short of its theoretical delivery by an' amount equivalent to the slip r.p.m. The motor' cannot turn out r.p.m. for Huid it did not receive, so it will show a shortage equal to the slip r.p.m. it did not v'receive' plus" its own slip r.p.m. In other words, a loss equal to theV sum of the slip r.p.m. of both units.

By placing a hydraulic slip compensating valve in a hydraulic circuit in parallel with a pump, the equivalent of additional slip is added 'to the' circuit by the valve, see slip diagrams, Fig. 8. For a system incorporating a pump uid ow through the system coincides with the arrows marked P. The pump inV forcing iluid to ilow in the direction of the arrows P raises the pressure in the system from Po to PL, but the bleed-out volume QBo, that is, the volume metered-out of the system can only flow' from PL to P0 (from high to low pressure) through the'valve.

The differential pressure PL-Po is the same in both legs of Fig. 8, therefore, a given pressure PL will result in a total slip volume equal to the pump slip volume Qs, plus the bleed-out volume QBo. The sum of the two is equal to Qs max. From Fig. 8 it is evident that Qs plus QBo always equals Qs max. irrespective of the pressure. Qs max. as previously pointed out is a constant for the system. B'yc'onv'ertin'g the slip volume Qs max. to slip r.p.m. and subtracting the so derived slip r.p.m. from the actual pump r.p.m., the elective speed of the pump in r.p.m. is obtained.

Particular attention is called to the fact that a variation in pressure no longer causes the flow rate to vary. The unit delivers a slightly reduced volume of fluid, that is, somewhat less than the max. possible, but the uid delivered is at a constant rate of llow, irrespective of pressure variations.

Response to a change of stroke in a Variable delivery pump is immediately reflected in a proportional increase or decrease in the rate of flow and changes in the ilow rate due to changing loads are automatically cancelled.

Because the demands of hydraulic slip no longer draw on the volume being delivered to the system, but on the volume by-passed by the slip compensating valve, the danger of stalling, that is, the danger of ceasing to pump no longer exists in the event sudden pressure increases occur as a variable delivery pump approaches zero delivery.

In commercial practice the slip volume of a hydraulic motor can readily be held to 3% at 1000 p.s.i. under which conditions the additional loss due to the slip compensator is only 1%, of 1% with respect to full load.

The member 24 is so arranged that it can oat radially without binding the reciprocating dierential plunger and can expand, without binding, between the covers l5, 16. A hole 66 in the spring calibrator 62 allows' a pin 67 to pass through it with ample radial clearance. Thepin 67 at one end bears against the cover I5 while the other end is slidably inserted in a hole S7 in the upper endwith reference to Fig. l-of the central member 24. The hole 87 `also contains a spring 68 which bears against the pin and holds it against the cover 15 while bearing against the bottom of the hole S7 to hold the port 99 in the central member at all times in relative alignment with the plunger head 23 by means' of the thin walled, and therefore springy tube 3l, without causing the central member 24 to bind in the sliding head 23. To assure proper alignment between the port 99 and the plunger head 23 a washer 69 is ground to the proper thickness while assembling the unit. Bushing 70 is brazed to the tube 31 acecho? v 11 and 'provided with an O ring 71 to prevent leakage from boreA 2,0 tothe hole 72. Backlash must be eliminated to be sure that the capacity once set, does not fluctuate but remains constant regardless of disturbances and despite the fact that a definite clearance must be maintained between the teeth 48-49 in order to provide variable viscous ow passageways 50 between them. Another source of backlash and variable clearance is the sliding fit between the plunger heads 21-23 and the bores 19-20. The seepage past a plunger with full excentricity-that is, when the O.D. of the plunger and the I.D.,of itsk bore are in contact-is 2.5 times as great as the seepage past one that has zero excentricity, that is, one that is fully centered. If the plunger can move around at random, in its clearance space in the bore, seepage will be erratic and cannot be compensated for.

By applying torque to the diierential plunger it will attempt to rotate within its guiding bores 19-20. If it cannot so rotate, the torque applied will cause the entire assembly to pivot about the point of restraint until the clearance in the bores is taken up and the assembly is in contact with the bores along a line parallel to the axis.

Leakage will increase somewhat over the irreducible minimum but the advantage gained is that it will not be erratic but very nearly constant and therefore readily compensate for. Wear will also have little inuence on the constancy of any leakage. To eliminate backlash and variable clearances in the valve under consideration, a carefully measured clockwise torque, see arrow in Fig. 2, is applied to the spring calibrator 62, which is free to rotate 011V antifriction bearing 63. The torque is applied by means of a spring 84 and transferred through the extension spring 89 and the tting 64 to the center section 22 of the differential plunger, causing one of its teeth 49 to strike the tooth 76 of the lever 73 and by reaction force the diierential plunger assembly in contact with the bores 19 and 20 at a point coinciding approximately with the arrow 81 of Fig. 2, and thus hold'the assembly from drifting about in its clearance space.

To further eliminate play and backlash, a spring 82 holds the lever 73 in iirm rattle proof engagement with the adjusting screw 78 and a spring 83 eliminates play both in the threads of the adjusting rscrew 78 and the pivot 74.

What I claim is:

l. A hydraulic slip compensating valve having an inlet for fluid of variable pressure and an outlet for fluid of variable pressure and means responsive to the pressure differential between said inlet and outlet, said means comprising: a valve body having a channeled portion in a part thereof, a housing at one side of said body incorporating said inlet and having an inlet port, a regulating valve in said housing, a hydraulically actuated spring loaded differential plunger within said valve body having channels on a portion thereof adapted to cooperate with the channeled portion of said valve body to provide viscous flow passageways and regulate the length thereof proportional to said pressure dilerential, lan inlet cham ber surrounding the intake ends of said variable length passageways; an axially disposed member extending through said differential plunger, spaced capillary sealsl in said dilerential plunger defining an annular space inj communication with said outlet, said axial member having an'annular port adapted to cooperate with one of said capillary seals and thereby generate avariable control pressure under the action of said pressure dilerential applied across the ends of said seal; passageways for cornmunicating the control pressure in said annular port to one end of said pressure regulating valve, passageways connecting the other end of said regulating valve to said inlet chamber; said inlet in said housing communicatingA with opposing ends of said differential plunger, said pressure regulating valve and with the inlet port to said Leo regulating valve in said housing, an outlet port in said housing and apassageway communicating with said inlet chamber, the ends opposite the intake ends ofsaid variable passageways terminating in an outlet chamber, means' connecting said outlet chamber with said annular spacev thereby communicating the outlet pressure thereto, and a housing at the other side of said valve body incorporating said outlet, Vsaid outlet chamber being connected to said outlet. Y

2. A hydraulic slip compensating valve having an inlet for liuid of variable pressure and an outlet for fluid of variable pressure and means responsive to the pressure differential between said inlet and outlet, said means comprising a valve body having a channeled portion in a part thereof and an inlet chamber and an outlet chamber, a hydraulically actuated spring loaded differential plunger within said valve body and channels on a portion thereof adapted to co-operate with the channeled portion of said valve body to provide viscous llow passageways and regulate the length thereof, a stationary member disposed centrally of said differential plunger and provided with an annular port, said differential plunger at both Vends thereof forming a capillary seal with said central member and in the region of said annular port adapted to generate a variable control pressure under the action of said pressure diierential; a pressure regulating valve, passageways for communicating the control pressure from said annular port to one endY of said pressure regulating valve, passageways connecting said other end of said regulating valve with the inlet chamber of said variable length passageways; said regulating valve having an inlet port and an outlet port, said inlet communicating with the ends of said diierenital plunger and with said inlet port, and a passageway connecting said outlet port with the inlet chamber of said variable length passageways, the opposite end of said variable passageways communicating with said outlet.Y

3. A valve of the character referredv to having an inlet for uid of variable pressure and an outlet for iluid of variable pressure and means responsive, to the pressure differential between said inlet and outlet, said valve comprising a valve body incorporating said outlet and aY housing incorporating said inlet, a dilerential plunger within and cti-operating with said valve body to provide viscous ilow channels, said plunger being in communication with said inlet and outlet and hydraulically actuated to regulate the volume of viscous flow; a stationary member extending through said plunger and provided with an annular port, said plunger forming capillary seals with said member for generating a variable control pressure under the action of said pressure dierential; a pressure regulating valve in said housing, passageways for communicating the control pressure to one end of said regulating valve; passageways connecting the other end of said regulating valve with the inlet side of said viscous flow channels; said housing having an inlet port and an outlet port adapted to be controlled by the movement of said pressure regulating valve, a passageway connecting the inlet in said housing with said inlet port; and a passageway connecting said outlet port with the inlet end of said channels, the opposite ends of said channels communicating with the outlet from said valve body.

4. A valve of the character referred to comprising a valve lbody having a channeled portion in a part thereof and an outlet for uid of variable pressure; a housing provided with an inlet for iluid of variable pressure; a differential plunger within said valve body having channels on a portion thereof for co-operation with the channels in said body to regulate the length thereof and provide viscous iow passageways therethrough, said housing having an inlet port communicating with said inlet and an outlet port, said inlet communicating with the ends of said dilerential plunger to actuate the same hytial plunger forming spaced capillary seals therewith, and having an annular port, and in the region of said 'port adapted to generate a variable control pressure under the action of the pressure differential between said linlet `and outlet, said housing having a passageway connecting said outlet port with the inlet side of said channels, ya pressure-regulating valve operable relative to said ports, means connecting said annular port to one end of said pressure regulating valve, and means connecting the other end of said regulating valve with the inlet side of said variable length channels, the outlet ends of said channels communicating with said outlet.

5. A valve of the character referred to, comprising a valve body having an linlet for uid of variable pressure and an outlet for uid of variable pressure, a differential plunger in said valve body responsive to the pressure differential between said inlet and outlet and in communicatiou at the top `and bottom thereof with said inlet, said plunger having means for co-operation with said body to provide variable length viscous flow passageways and being hydraulically actuable to regulate the rate of ow through said passageways, a stationary member extending through said plunger and provided with an -annular port adapted to generate a variable control pressure by action of said pressure differential; an inlet port in said valve body communicating with said inlet, an outlet port, a passageway connecting said outlet port with the inner ends of said channels, a valve operable relative to said ports for regulating the pressure in parts of said valve body, and means for communicating the control pressure from said annular port to said regulating valve.

6. A valve of the character referred to, comprising ya valve body having an inlet for uid of variable pressure and an outlet for iluid of variable pressure, a differential plunger in said body responsive to the pressure differential between said inlet and outlet and in communication at the top and bottom thereof with said inlet, said plunger having means for co-operation with said body to provide variable length viscous flow passageways and being operable in one direction to regulate the rate of ow through said passageways and in another direction to vary the capacity of the valve, a stationary member extending through said plunger and provided with an annular port adapted to generate a variable control pressure by action of said pressure dilferential; an inlet port in said valve body communicating with said inlet, -an outlet port, passageways connecting said outlet port with the inner ends of said means, a valve operable relative to said ports for regulating the pressure in said valve body, and passageways for communicating the control pressure from said annular port to said regulating valve, the outer ends of said means communicating with said outlet.

7. A valve of the character referred to, comprising a valve body having an inlet for fluid of variable pressure, and an outlet for fluid of variable pressure; a springloaded differential plunger in said body responsive to the pressure dilerential between said inlet and outlet and in communication at the top and bottom thereof with said inlet, said body and differential plunger provided with channels adapted for mutual engagement by the hydraulic actuation of said plunger to establish viscous flow passageways and regulate the length thereof, a stationary member extending through said plunger and forming spaced capillary seals therewith to generate a variable control pressure by action of said pressure differential, said member having an annular port, an inlet port communicating with said inlet, an outlet port, a passageway connecting said outlet port with the inner ends of said channels, a regulating valve operable relative to said inlet and outlet ports, and means for communicating pressure to both ends of said regulating valve; the outer ends of said channels communicating with said outlet.

8. A hydraulic slip compensating valve having an inlet for fluid of variable pressure and an outlet for fluid of variable pressure and means "responsive to the .pressure dilferential between said inlet andoutlet, said means comprising; a valve body, a channeled portion in apart of said valve body, anda chamber surrounding the intake end of said channeled portion; a spring-loaded differential plunger within said valve body and at opposite ends in communication with said inlet, said plunger having means for co-operation with the channeled portion in said valve body to provide viscous ow passageways and regulate the length thereof; an axially disposed member extending through said plunger, capillary seals in said plunger adapted to co-operate with said axial member to dene an annular space in communication with said outlet, said axial member having an annular port for cooperation with one of said seals to generate a variable control pressure under the action of said pressure differential; an -inlet port in communication with said inlet, lan outlet port, a regulating valve operable relative to said ports, passageways for communicating the control pressure in said annular port to one end of said regulating valve, passageways connecting the other end of said regulating valve with said chamber, a passageway connecting said outlet port with said chamber, said variable length passageways terminating in an annular space, and means connecting said yannular space with said outlet to communicate the outlet pressure thereto.

9. A slip compensating valve having an inlet for lluid of variable pressure and an outlet for fluid of variable pressure and means responsive to the pressure differential between said inlet and outlet, said means comprising: a valve body; a spring suspended differential plunger within said valve body and at opposite ends thereof in communication with said inlet; said body and said plunger provided with mutually cooperating means to provide viscous ow passageways; a chamber in communication with the intake end of said viscous ow passageways, said viscous ilow passageways terminating in said outlet; an axially disposed member extending through said plunger, capillary seals defining an annular space between said plunger and said axial member, said annular space in communication with said outlet, said ,axial member having an annular port for co-operation with one of said seals to generate a control pressure under the action of said pressure differenti-al, an inlet port communicating with said inlet, an outlet port communicating with said chamber, a regulating valve, means for conducting the control pressure from said annular port to one end of said regulating valve, and means for connecting said chamber with the other end of said valve for operating said regulating valve relative to said ports.

10. A slip compensating valve having an inlet `for fluid of variable pressure and an outlet for uid of variable pressure, said valve comprising a valve body; means dening serrated fluid metering capillary passageways within said valve body; means defining la variable controlpressure generating capillary passageway within said valve body; plunger means in said valve body and respons-ive to the pressure dilerential between said inlet and outlet for varying the lengths of said serrated fluid metering capillary passageways and the length of said variable controlpressure generating capillary passageway in unison and in direct proportion to said pressure differential; means converting the variations in length of said control-pressure passageway to non linear control-pressure values represented by the formula PC:PL(1 PL max.

ajszsagways.: at a ratevadequateftomaintain a pressure drop in said uid metering passageways equal Ito the in-I il References Cited in the le of this patentV UNITED STATES PATENTS Roth et a1. Y June s, 1934i` Douglas Dec. 14, 1937 Terry Apr. 24, 1945 Poitras et al. Apr. 29, 1947 

